Abstract: Featured with high energy density and sound safety, solid-state lithium-ion battery is the key to breaking through the bottleneck shackling battery technology, gathering wide attention from academia and industry. Solid-state electrolytes are the core of solid-state batteries, among which polyethylene oxide (PEO) polymer solid-state electrolyte excels at improving electrode interface compatibility and is one of the most potential electrolyte materials. This paper systematically elucidated the synergistic effect of PEO with inorganic modified fillers and its influence on ion transport and interfacial compatibility of composite solid-state electrolytes. Following an overview of the PEO-based composite solid-state electrolyte, the mechanism of ion transport was discussed. Then, the design, preparation, performance, and mechanism of PEO-inert filler and PEO-active filler composite solid-state electrolyte systems were reviewed respectively. Finally, an outlook on the future development and optimization design of composite solid-state polymer electrolytes was presented.